1. Field of the Invention
The present invention discloses a subsurface safety valve which can be either pressure differential operated (direct acting) or closed in response to an electromagnetic signal.
2. Description of Related Art
Direct acting subsurface safety valves, which are closed by an increase in the fluid flow rate through the valve, are shown in U.S. Pat. Nos. 3,070,119 invented by George M. Raulins and 3,126,908 invented by George C. Dickens. Both of these patents disclose using a ball type detent mechanism to hold the respective valve closure means open until the flow rate through the respective valve exceeds a preselected value. U.S. Pat. Nos. 3,070,119 and 3,126,908 are incorporated by reference for all purposes within this application.
A direct acting subsurface safety valve, which is closed by a preselected rate of pressure differential change, is shown in U.S. Pat. No. 4,339,001 invented by James H. Paschal, Jr. This patent discloses a ball type detent mechanism to hold the valve open until the rate of change of fluid pressure within the valve exceeds the preselected value. U.S. Pat. No. 4,339,001 is incorporated by reference for all purposes within this application. Another direct acting safety valve is disclosed in U.S. patent application Ser. No. 06/824,779 filed Jan. 31, 1986 now U.S. Pat. No. 4,664,195.
Various types of direct acting subsurface safety valves are commercially available under the trademark STORM CHOKE.RTM., registration number 695,910, assigned to Otis Engineering Corporation.
One problem with the use of direct acting safety valves is the ability of the valve to distinguish between fluctuations in fluid flow during normal production of the well and a transient flow condition caused by an emergency at the well surface. This problem is particularly difficult with respect to high flow rate gas wells. One advantage to direct acting safety valves is that they can be installed at deep depths in a well. At such depths, the pressure changes due to normal flow through the safety valve may be close to the pressure changes during emergency flow conditions. An important feature of the present invention is the ability to precisely adjust a direct acting safety valve to distingusih between a small pressure difference which is acceptable and a small pressure difference which indicates an emergency condition. For example, with a flowing bottom hole pressure of 2012 psig, a normal flow pressure difference through the safety valve might be 30 psig, while a difference of 35 psig would indicate an emergency condition. The normal flow rate for such wells might be 15 million to 75 million cubic feet of gas per day.
U.S. Pat. No. 4,161,215 discloses a solenoid operated safety valve which can be opened and closed in response to an electrical signal from the well surface. U.S. Pat. No. 4,617,960 discloses a system for closing a subsurface safety valve in response to an electromagnetic signal from the well surface. Both of these patents are incorporated by reference for all purposes within this application.